In many integrated circuit applications, an operating parameter of an analog or mixed-signal circuit block is determined based at least in part on the value of an internal resistor.
By way of example, a voltage-controlled oscillator (VCO) may include a ring oscillator that is formed of a controllable ring of inverter stages which utilize one or more internal resistors as load devices. Such a VCO may be utilized as an element of a phase-locked loop (PLL) in a clock recovery circuit or other type of circuit. The free-running frequency of the ring oscillator strongly depends on the internal resistor value, at least in part because the associated capacitance value does not vary as much as the resistor value.
A problem that arises in applications such as those described above is that the resistor value is typically subject to an excessively large variation within a given integrated circuit manufacturing process. As a result, for any particular integrated circuit design, integrated circuits manufactured using the same process can have significant differences between the values of their respective internal resistors, and the associated circuit operating parameters.
This problem leads to operating parameter error and other degradation in the achievable performance of the integrated circuits, thereby adversely impacting the production yield of the integrated circuit manufacturing process, and increasing device cost.
Conventional techniques have been unable to provide an adequate solution to the problem of excessive variation in internal resistor value. For example, such techniques generally fail to provide an efficient mechanism for determining the actual value of a given internal resistor in a particular integrated circuit.
A need therefore exists in the art for techniques which permit internal resistor values to be determined in an integrated circuit, so that appropriate adjustments can be made to associated circuit operating parameters in order to account for the actual values.